krakatau Volcano tour

Krakatoa

Harbour wave

Krakatoa represents the most violent volcanic eruption in recent human history, resulting in an estimated death toll of 36,000. Though Krakatoa was uninhabited, the adjacent islands felt the force of the eruption, with devastating consequences.

The greatest loss of life came not from the volcano itself but giant tsunamis up to 40 metres high, generated when the flanks of the volcano slid into the sea. The closest islands to the eruption were completely submerged by a series of giant waves. To the northeast of Krakatoa lay the island of Sebesi. Here, all vegetation was uprooted and 3000 people were washed out to sea. Over 80 kilometres away, on the Thousand Islands, a wall of water 2 metres high swept across the land.

Within the Sunda Straits, numerous ships accurately recorded the eruption and the tsunamis. One such vessel was the Gouverneur Generaal Loudon. On the morning of the Monday, she was sheltering from the ferocity of the eruption in the harbour of Lampong Bay near Telok Betong in Sumatra, 65 kilometres northeast of Krakatoa. The following is an eyewitness account from onboard the ship when the tsunami struck:

'Suddenly we saw a gigantic wave of prodigious height advancing toward the seashore with considerable speed. Immediately, the crew managed to set sail in face of the imminent danger; the ship had just enough time to meet with the wave from the front. The ship met the wave head on and the Loudon was lifted up with a dizzying rapidity and made a formidable leap. The wave continued on its journey toward land, and the benumbed crew watched as the sea in a single sweeping motion consumed the town. There, where an instant before had lain the town of Telok Betong, nothing remained but the open sea.'

Pyroclastic flows

While tsunamis were responsible for the majority of fatalities around Krakatoa, over 4500 deaths were attributed to the volcano's deadly pyroclastic flows. Meaning 'fire-broken', pyroclastic is the name volcanologists give to the dense hot flows of ash and rock that can travel down the flanks of a volcano at frightening speeds. Pyroclastic flows form when the eruption column, which contains vast amounts of dust, ash and rock (collectively know as tephra), collapses under its own weight when gases erupting from the volcano can no longer support the column.

The amount of tephra generated by the eruption of Krakatoa is thought to be to the order of 20 cubic kilometres. That's 20 times the amount generated by the 1980 eruption of Mount St Helens in the US.

The pyroclastic flows on Krakatoa were truly awesome. Once the column began to collapse, nothing could stop the ensuing calamity. At over 100kph, the tumultuous incandescent cloud would have raced down the sides of the volcano. Incredibly, the flows were able to travel across the waters of the Sunda Straits and remain hot enough to kill 2000 people 40 kilometres away in southern Sumatra. It's thought that when the base of the pyroclastic flows came into contact with the sea, a considerable amount of steam was generated which greatly enhanced the fluidity of the flow.

The Gouverneur Generaal Loudon, was blasted by pulses of hot searing winds and tephra that roared across the sea at near hurricane force. Luckily, the ship was just far enough away to escape spontaneous combustion due to intense heat. Closer towns, villages and ships were not so